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3126 Caterpillar

S

Sprint 6

Well-known Member
I have a 1998 3126 Cat that lopes at idle cold. I have changed out the fuel filters. I also changed the oil and drained the high pressure oil rail and reservoir. Once it is completely warm, it idles fine. It also runs fine off idle, except with smoke under load. No check engine light on and the intake heater is working. Any ideas on where to go next?
 
Could be your Huey pump, if it is, it's pump and injectors, don't ask me how I know! Hope it's something simple for you
 
High miles/hours?

Does the lope go away when you raise the idle slightly?

Does the engine otherwise run well and have good power? If it makes good power, don"t touch the injectors!

Likely you have some worn thrust washers in the governor, or some wear/binding in the fuel injector rack.

Even touching the injectors on this engine is a huge PITA, if you pull them from the cups you have to (normally) ream the cups with CAT tooling or replace them and seat them with more CAT tooling.

Otherwise aeration of the fuel from blowing combustion gas past the tip is a problem, (if the injectors are not seated in the copper cups) and this usually results in low power.

Dealt with many of these in marine applications but never messed with a truck application.
 
I would lean towards injectors as the cause but would not say change them unless the idle problem is unbearable. OR does the engine have lots of blowby? The c-7s which are the 3126 successor are known to break rings and score the cylinder walls and this can cause rough idle.I think the 3126 also breaks rings(250,000mi). These engines do not have sleeves so you have to have the block bored and sleeved. Mark
 
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